The purpose of this study is to determine if ibudilast is effective in reverting patients with medication overuse headache suffering chronic daily headache back to their original episodic headache pattern.

Response defined as ≥ 30% reduction in headache days/month or headache index from baseline. Expressed as percentage of patients who saw a ≥ 30% reduction in headache index after ibudilast treatment (at week 8) and NNT, number of patients treated to see 1 patient "respond".

It has been established that excessive intake of medications used to treat primary headaches, particularly those containing opioids, can induce a form of secondary headache, known as medication overuse headache (MOH). Despite the significant clinical impact of this condition the mechanisms behind MOH remain poorly understood, guidelines for treatment are lacking, and relapse is common.

Recently, it has been recognised that repeated opioid exposure can facilitate pain by activating glia, the immunocompetent cells of the central nervous system, resulting in opioid-induced hyperalgesia (OIH).

The investigators hypothesise that MOH represents a form of OIH in this susceptible patient group - repeated activation of nociceptive pathways by frequent headaches interacts with the opioid induced pro-inflammatory actions of activated glia to produce chronic daily headache (CDH).

This double-blind, randomised, placebo controlled pilot study will investigate the use of ibudilast, a know attenuator of glial activation, in the treatment of medication overuse headache.

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Please refer to this study by its ClinicalTrials.gov identifier: NCT01317992